Investigation of agglomeration and sedimentation of PEFC electrode slurries by a laminated microfluidic device

Abstract

A film-laminated microfluidic device was fabricated to analyze an electrode slurry used to form a porous electrode of polymer electrolyte fuel cells, and sorting of particles in the slurry was demonstrated. The electrode slurry contains carbon black and polymer electrolyte. Agglomerated particles in the slurry can affect the porous structure, which contains micro-cracks, surface roughness, and inhomogeneous pore size distribution, and resultant cell performance. The agglomerated particles settle down faster than small particles based on Stokes’ law. Therefore, in the present study, the microfluidic device, which has a flow channel with top and bottom branches of inlet and outlet in the direction of gravitational force, was used to sort agglomerates. A silica slurry was supplied, and the sorting of single-micrometer scale particle was demonstrated. The sorted particles in the flow channel were observed by optical microscopy. Sorting efficiency decreased with increasing flow rate. This result was consistent with a numerical simulation. Electrode slurries with/without ultrasonication were supplied to the microfluidic device and were evaluated in the same way. A large number of the agglomerated particles were successfully sorted to the bottom branch of the outlet. The slurry with ultrasonication showed a smaller number of agglomerated particles than the slurry without ultrasonication because the agglomerated particles were broken down into smaller particles by generation and demise of cavitation in the ultrasonication process. The extracted agglomerates were directly observed by scanning electron microscopy. Agglomerated particle size was in several single micrometers.

Keywords

• polymer electroyte fuel cell
• electrode
• slurry
• microfluidic device
• sedimentation
• agglomerate